There has been a trend in the coating art in general to attempt to utilize coating compositions which contain higher and higher solids content. In addition to utilizing less solvent to prepare the coating compositions, less energy is required to drive off the solvents during the curing stage after the composition has been applied to the substrate. However, the higher solids content composition can cause countless problems both in handling prior to the application to the substrate and in the actual application of the coating composition. This poses particular problems when the application of the enamel to the wire is done using felt applicators, which in some applications is the preferred technique.
This preferred technique, which gives best results, utilizes a felt pad to uniformly, concentrically apply the enamel to the substrate wire. Only those enamels which flow smoothly and evenly through the felt and onto the wire can be used. Typically, the viscosity of these materials has to be below 40 centipoise (cps). Enamels with high viscosities will clog the felt pad thereby restricting the flow of the enamel through the felt pad onto the wire. This will result in lower wire speeds and lower builds than desired. Since most of the polymers do not have viscosities within the prescribed range, they are diluted with a solvent, thereby lowering their solids content considerably. These solvents necessitate increased costs, produced environmental and occupational hazards as well as an increase in the number of passes through the applicator required to attain the desired thicknesses of the coating.
Accordingly, what is needed in this art is a coating method particularly adapted to coating magnet wire which overcomes such problems.